The broad objective of this renewal application for a Program Grant is to gain further insight into the biochemistry of aging by investigating the integrity of a select group of regulatory mechanisms. Project I concerns the role of insulin in the delayed adaptation in hepatic glucokinase activity following administration of glucose to aging Sprague-Dawley rats. Synthesis of proinsulin, conversion of proinsulin to insulin, secretion of insulin, and characterization of various hormone forms and metabolites will be studied in an attempt to identify the biochemical event whose modification is expressed as delayed secretion of insulin in response to glucose. Project II concerns the correlation between longer length of species lifespan and decreased susceptibility to chemically induced mutagenesis of fibroblasts grown in culture. Ability to induce mutagenesis by DMBA and other drugs, metabolism of DMBA to water-soluble products, and regulation of specific drug-metabolizing enzymes will be studied in fibroblast cultures derived from young adults of several species, from Sprague-Dawley rats of different ages, and from humans afflicted with progeria and Werner's syndrome. Project III concerns the reduced binding of steroid hormones to their hepatic receptor proteins in aging Sprague-Dawley rats. Efforts will focus on the mechanism of activation of the cytoplasmic hormone-receptor complex for nuclear transfer. Project IV concerns the characterization of mRNA isolated from aging Sprague-Dawley rats. Proinsulin mRNA will be translated in wheat germ and ascites systems, and the complementary DNA synthesized by reverse transcriptase will be subjected to hybridization studies.